(1) Field of the Invention
This invention relates to coastal energy absorption devices for absorbing the kinetic energy of the floating bodies such as ships approaching a coast line.
(2) Description of the Prior Art
Fenders are well known as the devices for absorbing the kinetic energy of ships approaching a coast. These are made of spring materials and are provided on the sides of the coast walls or pier walls so that the impact energy of the ships approaching these walls is absorbed by the springs in the form of displacement energy. Recently, since the ships are becoming larger in size, the spring constants of the fenders are also being increased.
However, if the spring constants of the fenders are increased, although large amounts of kinetic energy can be absorbed from large ships the reactive force on the shore or pier wall will also become very large thereby requiring that these walls be built considerably stronger.
Furthermore, when the fender spring constants are increased, the ratio of the spring constant of the fender to that of the mooring system will also become large, say, from 100:1 to 1000:1, as a result of which the movement of the moored ship due to the force of waves will not be limited to only swaying but also will consist of subharmonic motion which is large movement of the ship with oscillatory periods larger than the characteristic period of the mooring system which is caused by the spring constant of the mooring system being smaller than the spring constant of the fender and by the large assymetry of the mooring system.